A hydrodynamic bearing system essentially includes a bearing sleeve, a shaft accommodated in an inner cylindrical bore of the bearing sleeve and at least one radial bearing section provided between the bearing sleeve and the shaft with the aid of which the shaft and the bearing sleeve are supported rotatably with respect to each other. A bearing gap formed between the shaft and the bearing sleeve is filled with a liquid lubricant, preferably bearing oil.
A hydrodynamic bearing system is also provided with a hydrodynamic thrust bearing to take on axial loads. Such thrust bearing is essentially formed by a thrust plate preferably arranged at one end of the shaft and a corresponding cover plate. The cover plate forms the counter bearing to the thrust plate and seals the entire bearing system from below so that no lubricant can escape from the bearing system.
In the bearing arrangement described above, the thrust plate of the thrust bearing is located at one end of the shaft. The radial and thrust bearings are thus arranged one after the other along the rotational axis. The disadvantage of this type of arrangement is that the stability of the bearing is negatively influenced, particularly the vibration behavior of the rotor determined by the radial bearing's resistance to tilt.
It is therefore known to arrange the thrust plate about half way along the shaft, wherein an advantage of this arrangement is found in the fact that the span, i.e. the axial extension of the bearing arrangement, is increased. This improves the vibration behavior of the bearing and produces greater running stability, without having to accept increased friction losses as in the bearing arrangement mentioned at the beginning. A disadvantage of this arrangement is that due to the press fit provided between the shaft and the thrust plate, it is very difficult to push the thrust plate to the middle of the shaft. In doing so, there is a risk that the thrust plate adheres to the shaft due to local cold welding with the result that both the thrust plate and the shaft are rendered unusable.
To avoid these problems, it is known to connect the thrust plate to the shaft by means of welding. This type of bonding is revealed in JP 2000-324753. There is, however, the disadvantage and risk that the bearing system could become contaminated through welding residue which can cause damage to the bearing system. Due to the heat created in the welding process, there is an added risk that the thrust plate could be deformed and thus rendered unusable.
Another possible solution is to form the thrust plate and the shaft as one piece. Manufacturing such an integral component with the required tolerances, however, involves a very complex and expensive process.